1、扩展运算符...
将一个数组转为用逗号分隔的参数序列
console.log(...[1,2,3]); //1 2 3
用法：
（1）字符串转换为数组
split("")
[...str]
var str="hello";
console.log(str.split("")); //["h", "e", "l", "l", "o"]
console.log([...str]); //["h", "e", "l", "l", "o"]
（2）拼接数组
arr.concat(arr1,arr2,...)
[...arr1,...arr2,...]
var arr1=[1,2,3];
var arr2=[4,5,6];
console.log(arr1.concat(arr2)); //[1, 2, 3, 4, 5, 6]
console.log([...arr1,...arr2]); //[1, 2, 3, 4, 5, 6]
